967 research outputs found
Real-time propagators at finite temperature and chemical potential
We derive a form of spectral representations for all bosonic and fermionic
propagators in the real-time formulation of field theory at finite temperature
and chemical potential. Besides being simple and symmetrical between the
bosonic and the fermionic types, these representations depend explicitly on
analytic functions only. This last property allows a simple evaluation of loop
integrals in the energy variables over propagators in this form, even in
presence of chemical potentials, which is not possible over their conventional
form
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Thermodynamic properties of fluid n-D/sub 2/ in the 75 to 300 K and 2- to 20-kbar range
The hydrogen isotope deuterium is an important material for use in various energy technologies. This report is a summary of new pressure, volume, temperature, and sound velocity measurements of fluid n-D/sub 2/ in the 75 to 300 K and 2- to 20-kbar range. An equation of state (EOS) was fit to these data. The thermodynamic quantities, volume V, sound velocity v/sub s/, thermal expansivity ..cap alpha../sub p/, heat capacity at constant pressure C/sub p/, isothermal compressibility chi/sub T/, and molar entropy S, are given at 25/sup 0/K and 0.5-kbar increments over the range of measurements. Computer-drawn graphs of the isothermal pressure variation of these quantities are shown. Characteristics of the EOS at high temperature and pressure are determined and compared with theoretical and phenomenological equations of state
The effect of age and font size on reading text on handheld computers
Though there have been many studies of computer based text reading, only a few have considered the small screens of handheld computers. This paper presents an investigation into the effect of varying font size between 2 and 16 point on reading text on a handheld computer. By using both older and younger participants the possible effects of age were examined. Reading speed and accuracy were measured and subjective views of participants recorded. Objective results showed that there was little difference in reading performance above 6 point, but subjective comments from participants showed a preference for sizes in the middle range. We therefore suggest, for reading tasks, that designers of interfaces for mobile computers provide fonts in the range of 8-12 point to maximize readability for the widest range of users
Relaxed MHD states of a multiple region plasma
We calculate the stability of a multiple relaxation region MHD (MRXMHD)
plasma, or stepped-Beltrami plasma, using both variational and tearing mode
treatments. The configuration studied is a periodic cylinder. In the
variational treatment, the problem reduces to an eigenvalue problem for the
interface displacements. For the tearing mode treatment, analytic expressions
for the tearing mode stability parameter , being the jump in the
logarithm in the helical flux across the resonant surface, are found. The
stability of these treatments is compared for displacements of an
illustrative RFP-like configuration, comprising two distinct plasma regions.
For pressure-less configurations, we find the marginal stability conclusions of
each treatment to be identical, confirming analytic results in the literature.
The tearing mode treatment also resolves ideal MHD unstable solutions for which
: these correspond to displacement of a resonant interface.
Wall stabilisation scans resolve the internal and external ideal kink. Scans
with increasing pressure are also performed: these indicate that both
variational and tearing mode treatments have the same stability trends with
, and show pressure stabilisation in configurations with increasing edge
pressure. Combined, our results suggest that MRXMHD configurations which are
stable to ideal perturbations plus tearing modes are automatically in a stable
state. Such configurations, and their stability properties, are of emerging
importance in the quest to find mathematically rigorous solutions of ideal MHD
force balance in 3D geometry.Comment: 11 pages, 3 figures, 22nd IAEA Fusion Energy Conference, Geneva,
Switzerland. Submitted to Nuclear Fusio
Shock waves in two-dimensional granular flow: effects of rough walls and polydispersity
We have studied the two-dimensional flow of balls in a small angle funnel,
when either the side walls are rough or the balls are polydisperse. As in
earlier work on monodisperse flows in smooth funnels, we observe the formation
of kinematic shock waves/density waves. We find that for rough walls the flows
are more disordered than for smooth walls and that shock waves generally
propagate more slowly. For rough wall funnel flow, we show that the shock
velocity and frequency obey simple scaling laws. These scaling laws are
consistent with those found for smooth wall flow, but here they are cleaner
since there are fewer packing-site effects and we study a wider range of
parameters. For pipe flow (parallel side walls), rough walls support many shock
waves, while smooth walls exhibit fewer or no shock waves. For funnel flows of
balls with varying sizes, we find that flows with weak polydispersity behave
qualitatively similar to monodisperse flows. For strong polydispersity, scaling
breaks down and the shock waves consist of extended areas where the funnel is
blocked completely.Comment: 11 pages, 15 figures; accepted for PR
Statistical Analysis of Different Muon-antineutrino->Electron-antineutrino Searches
A combined statistical analysis of the experimental results of the LSND and
KARMEN \numubnueb oscillation search is presented. LSND has evidence for
neutrino oscillations that is not confirmed by the KARMEN experiment. This
joint analysis is based on the final likelihood results for both data sets. A
frequentist approach is applied to deduce confidence regions. At a combined
confidence level of 36%, there is no area of oscillation parameters compatible
with both experiments. For the complementary confidence of 1-0.36=64%, there
are two well defined regions of oscillation parameters (sin^2(2th),Dm^2)
compatible with both experiments.Comment: 25 pages, including 10 figures, submitted to Phys. Rev.
Comparative effectiveness of dual vs. single-action antidepressants on HIV clinical outcomes in HIV-infected people with depression
Objective: Depression is highly prevalent among people living with HIV/AIDS (PLWHA) and has deleterious effects on HIV clinical outcomes. We examined changes in depression symptoms, viral suppression, and CD4 + T cells/μl among PLWHA diagnosed with depression who initiated antidepressant treatment during routine care, and compared the effectiveness of dual-action and single-action antidepressants for improving those outcomes. Design: Comparative effectiveness study of new user dual-action or single-action antidepressant treatment episodes occurring from 2004 to 2014 obtained from the Center for AIDS Research Network of Integrated Clinical Systems. Methods: We identified new user treatment episodes with no antidepressant use in the preceding 90 days. We completed intent-to-treat and per protocol evaluations for the main analysis. Primary outcomes, were viral suppression (HIV viral load <200 copies/ml) and CD4 + T cells/μl. In a secondary analysis, we used the Patient Health Questionnaire-9 (PHQ-9) to evaluate changes in depression symptoms and remission (PHQ <5). Generalized estimating equations with inverse probability of treatment weights were fitted to estimate treatment effects. Results: In weighted intent-to-treat analyses, the probability of viral suppression increased 16% after initiating antidepressants [95% confidence interval=(1.12, 1.20)]. We observed an increase of 39 CD4 + T cells/μl after initiating antidepressants (30, 48). Both the frequency of remission from depression and PHQ-9 scores improved after antidepressant initiation. Comparative effectiveness estimates were null in all models. Conclusion: Initiating antidepressant treatment was associated with improvements in depression, viral suppression, and CD4 + T cells/μl, highlighting the health benefits of treating depression in PLWHA. Dual and single-action antidepressants had comparable effectiveness
Consistent Anisotropic Repulsions for Simple Molecules
We extract atom-atom potentials from the effective spherical potentials that
suc cessfully model Hugoniot experiments on molecular fluids, e.g., and
. In the case of the resulting potentials compare very well with the
atom-atom potentials used in studies of solid-state propertie s, while for
they are considerably softer at short distances. Ground state (T=0K) and
room temperatu re calculations performed with the new potential resolve
the previous discrepancy between experimental and theoretical results.Comment: RevTeX, 5 figure
The physical basis of natural units and truly fundamental constants
The natural unit system, in which the value of fundamental constants such as
c and h are set equal to one and all quantities are expressed in terms of a
single unit, is usually introduced as a calculational convenience. However, we
demonstrate that this system of natural units has a physical justification as
well. We discuss and review the natural units, including definitions for each
of the seven base units in the International System of Units (SI) in terms of a
single unit. We also review the fundamental constants, which can be classified
as units-dependent or units-independent. Units-independent constants, whose
values are not determined by human conventions of units, may be interpreted as
inherent constants of nature.Comment: 17 pages, to be published in European Physical Journal-Plus, The
final publication is available at www.epj.or
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